A discharge device for a shaft is known from WO 2015/032989 A2, said shaft comprising a flexurally elastic conductor made of a carbon fiber arrangement. The conductor is mounted to a holder, which is positioned relative to the shaft in such a manner that the conductor can rest on the shaft by forming an initial load. Thus, it becomes possible to discharge an electrostatic charge of the shaft via the conductor. The shaft can consequently be grounded via the conductor.
A disadvantage of the known discharge devices is that they have to always be installed adjacent to the shaft using a holder. Hence, there must always be sufficient installation space present for mounting the holder in conjunction with the conductor in the area of the shaft. Depending on the type of usage intended for the shaft, in particular when the shaft is mounted by means of rolling bearings, electrostatic charges can also be discharged from the shaft via the rolling bearings. These currents can also be discharged via the rolling bearings when a discharge device is arranged at the shaft at a distance to the rolling bearings. It has proven that a passage of electric current through a rolling bearing leads to progressing wear of the bearing rings and balls with increasing service life. In particular pittings as well as grooves can be observed at the bearing rings.
Using either ceramic or ceramically coated balls as insulators and/or electrically conductive grease in lubricated bearings is also a known technique for discharging vagrant currents. A transition resistance of the grease is then adjusted in such a manner that a current is no longer discharged via the balls but via the grease instead. A disadvantage of the conductive grease is its reduced lubrication properties, which results from adding conductive particles. Furthermore, the conductive grease can be negatively altered by high thermal stress and a passage of electric current. Occurring vagrant currents, for example, can decompose the grease via large fluctuations in temperature, thus making the grease useless. The grease's viscosity is also reduced by adding conductive particles.